A photoconductive semiconductor switch (PCSS) triggered with an ultra-short pulsed laser is a type of low-jitter ultra-broadband high-power switch device without potential spurious triggering caused by electro-magnetic interference. There are two operating modes of PCSS which depends on whether there is avalanche multiplication of photon-generated carriers, namely, the linear operating mode and the high-gain operating mode (also called the nonlinear mode or the lock-on mode). A traditional PCSS is composed of an anode, a semi-insulating substrate and a cathode. The semi-insulating substrate is usually obtained by highly compensating a low-resistivity semiconductor crystal with deep-energy-level impurities or defects, such as iron-doped GaN (GaN:Fe) and vanadium-doped SiC (SiC:V). Taking GaN for example, the resistivity of GaN crystal can reach a high level only by doping deep-energy-level Fe impurity with a concentration of more than 1017 cm−3. Thus, the GaN:Fe crystal can be used as the semi-insulating substrate of the traditional PCSS. However, the dark-state resistance of the traditional PCSS is remarkably nonlinear, which is mainly caused by the unavoidable high-concentration deep energy levels. Consequently, the dark-state leakage current of the traditional PCSS will significantly increase with the bias voltage increasing until the traditional PCSS is broken down. The leakage current of the PCSS biased with a dc voltage source restricts the dc withstand voltage capability. Furthermore, since the average drift velocity of the photon-generated carriers is usually proportional to the bias voltage, it also restricts the photocurrent peak of the PCSS
In addition, GaAs PCSS and InP PCSS can operate with the high-gain mode at a high bias voltage. The remarkable advantages of the high-gain operating mode lie in the fact that it can be triggered by a weak laser and the rising edge of the photocurrent pulse is much faster than that of the triggering laser, due to the avalanche multiplication of the photon-generated carriers. Therefore, said PCSS can choose a low-cost portable laser diode as the light source, rather than an expensive heavy pulsed power laser. The disadvantage of said GaAs PCSS and InP PCSS lies in the fact that when the PCSS operates in the high-gain mode, the PCSS is unable to turn off by itself in nanoseconds or even microseconds because the current is “locked on”, unless the bias electric field across said semi-insulating substrate can quickly reduce to the level below the threshold electric field for maintaining the high-gain mode. The existing solution to the above-mentioned problems is to use a low-duty-ratio high-voltage pulse source as the bias voltage source of PCSS, such as Marx circuit, which can inhibit the dark-state leakage current of PCSS and force the GaAs PCSS and InP PCSS to quit from the high-gain operating mode. However, since a high-voltage pulse source usually comprises several high-power devices and the impedance matching of the transmission lines between these devices is difficult, this kind of PCSS system is high in cost and poor in portability, especially when a high repetition rate is required.